1. Field of the Invention
The present invention relates to the field of electrical contact devices, such as multi-phase contactors. More particularly, the invention relates to a stationary contact structure for use in such devices and to a method for channeling current flow through such stationary contact structures.
2. Description of the Related Art
A variety of electrical contact devices are known for completing current carrying paths between a source of electrical energy and a load. Remotely operated devices of this type typically include an actuating assembly and a contact assembly. The actuating assembly typically includes an electromagnetic subassembly which produces a magnetic field when an energizing current is passed through an actuating coil. The magnetic field draws an armature into an actuated position, thereby opening or closing contacts in the contact assembly, depending upon whether the device is installed for normally-open or normally-closed operation. Upon release of the energizing current, the contact assembly returns to its normal position.
Electrical contactors of the type described above generally include movable and stationary contact structures in their contact assemblies. The stationary contact structures include terminals designed to be coupled to the source of electrical energy and to the load. The movable contact structures are designed to span the stationary contact structures, and thereby to complete a current-carrying path therebetween upon demand. The current-carrying path is thereby opened and closed by movement of the movable contact assembly.
Through opening and closing cycles of contact assemblies, arcs may be produced between contact pads which touch one another when the contactor is closed. Such arcing may be limited by appropriate design of the stationary and movable contacts, and is generally dissipated by splitter plate assemblies and the like. For example, electrical contactors have been designed to include multiple movable contacts per phase which close and open at different times. Thus, an arc contact may be made to make the electrical connection first, followed by closure of a shunt contact through which a current is primarily carried during steady state operation. Upon opening, the shunt contact is opened first, followed by opening of the arc contact. This structure permits the arc contacts to bear the anticipated arcing during opening and closing. Arcs are typically then lead away from the arc contacts on the stationary contact structure to splitter plates where the arcs are dissipated and cooled.
Attempts have also been made in the design of stationary contact structures to facilitate arc mobility from the stationary contact pads to dissipating structures, such as splitter plates. However, dynamics of arc mobility are influenced by a number of factors which may not be optimized in the stationary contact design. Such factors may include the influence of magnetic fields generated during opening and closing, gas dynamics in the vicinity of the stationary and movable contacts, and so forth. Conventional stationary contact structures, for example, employ a base plate and turnback arrangement, with a stationary contact pad being provided on an outer surface of the turnback. The turnback permits arcs to migrate from the stationary contact pad to a splitter plate stack upon opening and closing.
While such structures have provided relatively good performance, they are not without drawbacks. For example, conventional stationary contact structures including turnbacks tend to generate repulsive forces during steady state operation due to dissimilar orientation of fields in the movable contact spanner structure and in the stationary contacts, particularly in the turnback portion of the stationary contact. This repulsive force must be opposed by the magnetic holding field of the actuating assembly during steady state operation. Moreover, conventional stationary contact structures are typically manufactured by bending conductive metal plates and subsequently attaching contact pads to the plates. As a result of the manufacturing processes involved, optimal configuration of the stationary contact structure from the point of view of field orientations and arc migration to splitter plates may be impossible to obtain.
There is a need, therefore, an improved stationary contact structure for contactors and similar switching devices. In particular, there is a need for a structure which is both efficient to manufacture and provides the electrical and magnetic features of turnbacks, while permitting a reduction in forces exerted by an actuating assembly during making of the contact and during steady state operation. There is also a need for improved stationary contact structures which aid in thermal management of arcs produced during opening and closing phases of operation.
The present invention provides a stationary contact configuration designed to respond to these needs. The contact provides a conductive structure for leading an arc away from a stationary contact region, while reducing a magnetic field effect both during closure of a movable contact and during steady state operation. The stationary contact structures may be produced through an extrusion process, thereby facilitating creations of cross-sectional geometries which improve arc migration, thermal cooling, at the same time as reducing the pull-in and steady state forces required during operation with a movable contact. The stationary contact structures provided may assume various configurations, including arrangements which aid in establishing different current carrying paths during transient and steady state operation, and structures which facilitate arc mobility and thermal energy dissipation.
Thus, in accordance with the first aspect of the invention, a stationary contact is provided for an electrical contactor. The stationary contact includes a substantially planar base plate, a turnback and a contact pad. The turnback is electrically coupled to the base plate. The turnback includes a riser extending from the base plate and an arc guide extending from the riser over the base plate. The contact pad is secured to the riser. The riser extends in substantially linear orientation between the base plate and the contact pad. In a preferred configuration, the riser extends substantially orthogonally from the base plate. To obtain the desired geometry of the stationary contact structure, the base plate and the riser may be integrally formed by an extrusion process. The base plate may terminate at the riser, or may extend beyond the riser, such as for carrying current during steady state operation. The arc guide may descend from the level of the top of the riser, toward the base plate, for guiding arcs to a desired location in a splitter plate stack.
In accordance with another aspect of the invention, a stationary contact for an electrical contactor includes a base plate, a riser, and a contact pad. The riser is substantially planar, and is integral with the base plate, extending at an angle therefrom. The contact pad is secured to the riser at an end thereof opposite the base plate. The riser may extend substantially perpendicularly from the base plate. In a preferred configuration, an arc guide extends from the riser for guiding arcs from the contact pad. The riser and arc guide may be integral structures having different thicknesses for thermoconductivity purposes. A contact extension may project beyond the riser and may include a second contact pad, such as for carrying current during steady state operation.
The invention also provides the novel technique for making a stationary contact and an electrical contactor. In accordance with the method, a profile based component stock is extruded. The base component stock includes a base plate portion and a riser portion extending from the base plate portion. The stock is then cut to a desired width. At least one contact pad is secured to the riser portion. Integral arc guides, and turnbacks may be formed in the base component stock, and may include portions of different thickness, as well as portions which curve or descend toward a base plate section of the contact structure. Other contact pads may be secured to the stock, such as pads on a base plate extension for carrying current during steady state operation.
Moreover, the invention offers novel method for establishing and interrupting current carrying paths through stationary contacts in contactors and similar devices. In accordance with certain aspects of the methods, current is channeled through risers extending between base plate portions and turnback portions of the stationary contacts. Separate current carrying paths may be established for steady state operation, which extend primarily through the base plate portion and a current carrying extension thereof.